EUV mask absorber sidewall angle should be measured for mask Optical Proximity Correction and shadow effect estimation. Hence, verifying the three-dimensional profile of mask topography has become a challenge in EUV mask inspection. This paper evaluates EUV mask sidewall angle measurement by Field-Emission Critical Dimension (CD)-Scanning Electron Microscope (SEM) using JEOL JSM-7401F. SEM only produces two-dimensional gray images. Forming three-dimensional profiles from these images is a critical requirement for the sidewall angle measurement. To obtain three-dimensional information, absorber edge width has to be measured first to measure sidewall angle. We can calculate absorber sidewall angle with the exactly measured edge width and absorber height. Edge width narrows with steeper sidewall angle. We used the image processing function of Matlab to obtain absorber edge width accurately. In the end, every measured sidewall angle was compared to Transmission Electron Microscope (TEM) images to evaluate the validity of SEM results. Measured sidewall angles by SEM and TEM cross-section images have average tolerances of 0.62 degrees.
A new methodology using the admittance diagram is proposed for optimization of an antireflective layer (ARt) and the simple ARt optimizer with its own 2D and 3D dynamic graphic tools is developed. Under the methodology, the overall dependency of the reflectivity on optical properties of ARLs can be viewed from a single 2D graph, and the tolerance of process step for the optimally designed ARL can be evaluated geometrically. And also, the optimal condition of an ARt for DUV lithography process is determined by our optimizer and its performance is simulated from our own lithography simulator based on rigorous vector theory. Finally, the effect of ARLs are investigated experimentally, and their results are compared with simulation results.
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